Protease inhibitor proteins from plant

Cysteine protease inhibitor proteins from plants... 

While a few very potent non-peptide protease inhibitors (Pis) have been isolated from plants many plant protease inhibitor proteins (PIPs) have evolved to have protease interaction Kj values in the nanomolar and picomolar range. These extraordinary affinities derive from the matching of the PI protein amino sequence about the scissile peptide bond (Pl-Pl ) and evolution of adjacent sequences to fit and interact appropriately within the target protease active site [1, 120, 121]. The structure and function of the different classes of PI proteins from plants are succinctly but comprehensively reviewed below. 

A variety of aspartic protease inhibitor (API) proteins have been resolved from plants [122-135] of which the best characterized at the gene and protein level are those from Solanum tuberosum (potato) (Solanaceae) [124-134] (Table 4). The potato aspartic protease inhibitor proteins are typically about 190 residues (about 20 kDa), have 3 disulphide bridges, are homologous to the soybean trypsin inhibitor (Kunitz) family Pis [133] and can also inhibit trypsin [124-134] (Table 4). 

This review has succinctly summarized what is presently known of nonprotein and protein protease inhibitors from plants. The affinities of the non-protein inhibitors for particular proteases are generally much lower than those of plant protease inhibitor proteins (PIPs). Nevertheless the non-protein protease inhibitors may provide structure/activity starting points for development of pharmaceutically useful compounds of much higher affinity. The plant PIP literature has been comprehensively surveyed in this review. However electronic databases such as EMBL and SWISSPROT contain further accessible plant PIP sequences [581]. The array of potent plant PIPs reflects the co-evolution of plant defensive proteins and insect resistance [582]. Potent, stable, protease inhibitor proteins have potential transgenic crop agriculture applications as well as potential chemotherapeutic applications. 

Because plants cannot escape from insect injury, many plants protect themselves by producing defense proteins. Protease inhibitors, which protect plants by inhibiting the feed digestion of insects, are well-studied defense proteins. These protease inhibitors are induced in leaves distant from points of injury, indicating that signal substances are involved in systemic resistance induction in plants. 

Proteins are found in all organisms, play many roles, and vary widely in structure and properties. The enzyme ribulose 1,5-bisphosphate carboxylase (EC 4.1.1.39) is probably the world s most abundant protein, as it is the major protein present (up to 50%) in the leaves of plants (Ramshaw, 1982). However, in the following discussion, only those proteins with toxic or inhibitory properties to animals or fungi or other noteworthy activity will be discussed. Several groups of proteins from plants are known to be toxic to animals. The most important group of these is called lectins or hemagglutinins. Many legume seeds also contain protease (or trypsin) inhibitors (Weder, 1981). Similar compounds are found in plants of the Solanaceae (Ramshaw, 1982). 

In tomato and potato plants, two families of Pis have been identified that show wound-inducible expression. Within 48 h after wounding of leaves of these plants, up to 2% of leaf protein content is made up of protease inhibitors. Potato type I (Potl) inhibitors are not only expressed in wounded leaves but also in tissue of leaves away from the site of attack. ° This finding prompted the search for a hormone or inducing factor that carries the signal for enhanced inhibitor expression through the plant system. Systemin, an 18-residue peptide hormone, has since been reported to induce more than 15 genes of defense nature in tomatoes. ... 

Common technical approaches to plant proteomics investigations are the extraction and the purification of proteins from crude tissue (8) however, due to the presence of a number of proteases and a low protein charge, a protection against proteolysis is highly recommended by adding selected inhibitors. Then the removal of nonproteinaceous products is operated according to the nature of the plant tissue (see scheme on Figure 2). 

PROTEIN AND NON-PROTEIN PROTEASE INHIBITORS FROM PLANTS... 

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